DE19727866C2 - Device for controlling an internal combustion engine - Google Patents

Description

The invention relates to a device for controlling a Internal combustion engine, in particular an internal combustion engine with Direct fuel injection and / or largely dros selseless load control.

An internal combustion engine is known from DE 43 32 171 A1 with an intake tract in which a throttle valve is arranged and with an exhaust gas recirculation device that is an exhaust gas return valve includes. For each cylinder of the internal combustion engine An injection valve is provided for the fuel directly into the combustion chamber. A control device is provided the throttle valve and the exhaust gas recirculation valve controls. In operating areas of the internal combustion engine with Ab gas recirculation essentially turns the throttle valve into a brought constant partial opening position. In addition either regulating the air ratio to the setpoint Lambda = 1, the exhaust gas recirculation valve being the actuator is seen, or control of the recirculated exhaust gas depending on the fuel injection quantity or position the accelerator pedal or the amount of air sucked in.

However, the exhaust gas recirculation rate is set always only by controlling the exhaust gas recirculation valve. High exhaust gas recirculation rates in particular can be achieved with the known tax setup can only be set slowly. By recirculated exhaust gas becomes the combustion peak temperature during the combustion of the air-fuel mixture in the burner space reduced. The higher the proportion of the recirculated exhaust gas the more nitrogen oxide emissions are reduced. The efficiency of the internal combustion engine increases with the amount of the recirculated exhaust gas because less heat is transferred to the Cylinder walls are released and pump losses are reduced the.  

DE 196 31 112 A1 describes a control device for a Internal combustion engine known in which either a throttle valve pe is operated via a pneumatic valve and a controller is provided whose controlled variable is the stroke of its Actuator, an exhaust gas recirculation valve, or the controller and another controller are provided, the controlled variable is the degree of opening of its actuator, the throttle valve.

It is the object of the invention to provide a control device to create an internal combustion engine with which a pre entered high exhaust gas recirculation rate quickly and reliably can be put.

The task is characterized by the features of the independent patent claims 1 and 2 solved. The invention is characterized by this from that for the actuators throttle valve and exhaust back guide valve a pilot control device is provided, the Control variable is the exhaust gas flow rate. So can also during a transient operation of the internal combustion engine quickly the ever exhaust gas recirculation rate can be set. The invention allows the throttle to adjust the exhaust to control the return rate. So can by appropriate A position of a fresh gas partial pressure downstream of the Dros a very quick change in the exhaust gas recirculation rate can be achieved.

A first or second controller is provided, the rule of which size is the exhaust gas recirculation rate and that as the actuator Exhaust gas recirculation valve or the throttle valve is assigned. This enables a very precise adjustment of the exhaust gas return recirculation rate. If the actuator of the controller is the throttle valve, so can a very simple and therefore cheap exhaust gas recirculation valve are provided. The exhaust gas recirculation valve can then as a simple on / off valve without prior feedback from the warehouse be seen.

In an advantageous embodiment of the invention, the second pilot control depends on the throttle valve  of the speed and the ambient pressure. This has the intent part that the exhaust gas recirculation rate very quickly and also can be set precisely. The operating variables speed and ambient pressure are the main influencing factors, with the help of which an actuating signal for controlling the throttle valve can be determined to the desired exhaust gas recirculation rate adjust.

Further advantageous embodiments of the invention are in marked the subclaims.

Embodiments of the invention are described below Explained with reference to the schematic drawings. It demonstrate:

Fig. 1 shows an internal combustion engine with a control device according to the invention and

Fig. 2 is a block diagram of the control device.

Elements of the same construction and function are larger than figures provided with the same reference numerals.

An internal combustion engine ( FIG. 1) comprises an intake tract 1 with a throttle valve 10 and an engine block 2 which has a cylinder 20 and a crankshaft 23 . A piston 21 and a connecting rod 22 are assigned to the cylinder 20 . The connecting rod 22 is connected to the piston 21 and the crankshaft 23 .

Furthermore, a cylinder head 3 is provided in which a valve train with at least one inlet valve 30 , an outlet valve 31 and in each case one of the inlet valve 30 associated valve drive 32 a and one of the outlet valve 31 associated valve drive 32 b is arranged. The valve actuators 32 a, 32 b each comprise a camshaft, not shown, with a transmission device which transmits the cam lift to the intake valve 30 and the exhaust valve 31 . Means for adjusting the valve lift times and the valve lift curve can also be provided. Alternatively, an electromagnetic actuator can also be provided in each case, which controls the course of the valve lift of the intake and exhaust valves 30 , 31 .

An injection valve 33 and a spark plug 34 are also introduced into the cylinder head 3 . The injection valve 33 is arranged such that the fuel is metered directly into the interior of the cylinder 20 . The injection valve 33 can also be arranged so that the metering of the fuel takes place in the intake tract 1 . The internal combustion engine can also be designed as a self-igniting internal combustion engine. Then no spark plug 34 is provided and instead of an injection valve 33 , an injection pump and an injection nozzle are optionally provided. The internal combustion engine is shown in FIG. 1 with a cylinder 20 . However, it can also comprise several cylinders.

The internal combustion engine further comprises an exhaust tract 4 in which a catalytic converter 40 is arranged. The internal combustion engine has an exhaust gas recirculation device 5 with an exhaust gas recirculation pipe 50 which is guided from the exhaust tract 4 to the intake tract 1 . In the exhaust gas recirculation pipe 50 , an exhaust gas recirculation valve 51 is arranged. The exhaust gas recirculation valve 51 is designed as a lift valve. However, it can also be designed as a flap, for example.

A control device 6 for the internal combustion engine is seen before, the sensors are assigned to detect the various measurement variables and to determine the measured value of the measurement variable. The control device 6 determines one or more control signals depending on at least one measured variable, each of which controls an actuator.

The sensors are a pedal position sensor 71 which detects a pedal position PV of the accelerator pedal 7 , a throttle valve position sensor 11 which detects an opening degree THR of the throttle valve 10 , an air mass meter 12 which detects an air mass flow MAF and / or an intake manifold pressure sensor 13 which detects an intake manifold pressure MAP detects a temperature sensor 14 , which detects an intake air temperature TAL, a speed sensor 24 , which detects a speed N of the crankshaft 23 , an oxygen probe 41 , which detects the residual oxygen content of the exhaust gas and which assigns an air ratio LAM to it and a position sensor 52 , which detects the opening degree EGRV_AV of the exhaust gas recirculation valve 51 . Depending on the embodiment of the invention, any subset of the sensors mentioned or additional sensors can be present.

Operating variables include the measured variables as well as these conducted quantities, such as an exhaust gas temperature TEG, over a Map context or who is determined by an observer the one that calculates the estimates of the farm sizes.

The control units each include an actuator and an actuator. The actuator is an electromotive drive, an electromagnetic drive, a mechanical or another drive known to the person skilled in the art. The actuators are designed as a throttle valve 10 , as an exhaust gas recirculation valve 51 , as an injection valve 33 , as a spark plug 34 or as an adjusting device for adjusting the valve lift of the inlet or outlet valves 30 , 31 . The actuators are referred to in the fol lowing with the associated actuator.

The control device 6 is preferably designed as an electronic engine control. However, it can also comprise several control devices which are connected to one another in an electrically conductive manner, for. B. via a bus system.

In Fig. 2 is a block diagram of the preferred exporting is approximate shape of the control device 6 is shown. In a block B1, a desired indexed torque TQI_REQ is determined depending on the accelerator pedal value PV and the speed N.

The desired index is preferably determined torque TQI_REQ via a first map that depends from the pedal value PV and the speed N. In a comfort ler embodiment, the desired is determined indicated torque TQI_REQ additionally dependent on other operating variables such as the intake air temperature TAL or a cooling water temperature or an oil temperature.

In a block B2, a target value EGRR_SP of the exhaust gas recirculation rate is determined as a function of the desired indicated torque TQI_REQ and the speed N from a second map. The map values are optimized with regard to the efficiency of the internal combustion engine and with regard to the NOx emissions. An internal combustion engine with gasoline direct injection is in predetermined operating ranges, such. B. in the partial load, operated with an inhomogeneous very lean air-fuel mixture and high exhaust gas recirculation rate (up to 50%). In order to ensure the conversion of the NOx emissions by the catalytic converter 4 , the internal combustion engine is operated at predetermined time intervals (e.g. 1 minute) with a homogeneous air / fuel mixture and a low exhaust gas recirculation rate (e.g. <10%). The map values in the second map are therefore also dependent on an operating mode of the internal combustion engine - that is, homogeneous or inhomogeneous.

A block B3 comprises an observer who, through physical modeling of the intake tract 1 and the exhaust gas recirculation device 5, an estimate EGRMF_MOD of the recirculated exhaust gas mass flow through the exhaust gas recirculation pipe 50 , an estimate EGBP_MOD of an exhaust gas back pressure in the exhaust tract 4 , an estimate AMP_MOD of the ambient pressure and, if appropriate calculates an estimate MAP_MOD of the intake manifold pressure. Such a model of the intake tract 1 is described in WO 96/32579 A1, the content of which is hereby incorporated in this regard. Such a model of the intake tract 1 and the exhaust gas recirculation device 5 is described in the unpublished patent application by the same applicant WO 97/35106 A, the content of which is also included in this regard. For this purpose, the model is determined from the equation of state of ideal gases, the flow equation of ideal gases through throttling points, and a linear relationship between the intake manifold pressure and a mass flow into the cylinder 20 . The input variables of block B3 are the speed N, the air mass flow MAF, the intake manifold pressure MAP, the actual value THR_AV of the degree of opening of the throttle valve 10 , the actual value EGRV_AV of the degree of opening of the exhaust gas recirculation valve 51 , the intake temperature TAL and the exhaust gas temperature TEG. If no sensor for determining the exhaust gas temperature TEG is provided, the exhaust gas recirculation temperature can also be obtained from a map depending on the speed N and a load replacement size - for. B. an injected fuel mass per work cycle of the internal combustion engine or the air mass flow MAF - can be determined.

In block B4, an actual value EGRR_AV of the exhaust gas recirculation rate is determined depending on the estimated value EGRMF_MOD of the recirculated exhaust gas mass flow and the air mass flow MAF. The actual EGRR_AV value of the exhaust gas recirculation rate is preferred using the equation

calculated.

A first pilot control device 61 determines a reduced flow cross section ARED_EGRV at the exhaust gas recirculation valve 51 as a function of the target value EGRR_SP of the exhaust gas recirculation rate, the estimated value EGBP_MOD of the exhaust gas counterpressure and the intake manifold pressure MAP in the intake tract 1 . A first controller 63 is provided, the controlled variable of which is the exhaust gas recirculation rate and the control difference of which is the difference between the target value EGRR_SP and the actual value EGRR_AV of the exhaust gas recirculation rate.

The controller is designed as a PI controller. The control signal of the controller is a correction value DARED_EGRV of the reduced flow cross section at the exhaust gas recirculation valve 51 .

A block B8 comprises a further map from which a setpoint EGRV_SP of the degree of opening of the exhaust gas recirculation valve is determined depending on the sum of the correction value DARED_ERGV and the reduced flow cross section ARED_EGRV. The target value of the opening degree of the EGRV_SP Abgasrückführven TILs 51 is supplied to a position controller of the exhaust gas recirculation valve 51, not shown, which generates a control signal for the Ab gas recirculation valve 51st

A second pilot control device 62 is provided, the control variable of which is the setpoint EGRR_SP of the exhaust gas recirculation rate and the control signal is a reduced flow cross section ARED_THR of the throttle valve 10 . By means of the second pilot control device 62 , a very rapid setting of high exhaust gas recirculation rates is achieved. This is a major advantage if the internal combustion engine is operated alternately with an inhomogeneous air-fuel mixture and high exhaust gas recirculation rate and homogeneous air-fuel mixture and low exhaust gas recirculation rate with a constant load.

A calculation rule for determining the reduced flow cross section ARED_THR at the throttle valve 10 is described below. The EGRR_SP setpoint of the exhaust gas recirculation rate can alternatively be based on the equation

are calculated, where EGRMF is the recirculated exhaust gas mass electricity is.

Furthermore, the partial pressures in the intake manifold, that is to say in the intake tract 1 downstream of the throttle valve 10 , behave identically to the mass flows in stationary operation. The following applies:

where, P _{RG is} a residual gas partial pressure in the intake tract 1 , and P _{FG is} a fresh gas partial pressure in the intake tract 1 . Residual gases are the recirculated exhaust gases.

In a largely unthrottled operation, there is a slight pressure drop at the throttle valve 10 . The pressure drop at the throttle valve 10 can be determined with sufficient accuracy depending on the speed N. The following relationship applies:

where K _{P is} a first factor, which is preferably determined from a map as a function of the speed N. Equation 3 gives the equation after the intake manifold pressure MAP

MAP = K _P .AMP (4)

The equation results from equations (1), (2) and (4)

P _FG = AMP. (1 - EGRR_SP.K _P ) (5)

A linear approximation can be assumed between the air mass flow MAF and the fresh gas partial pressure P _FG in the intake tract 1 . The following equation applies:

MAF = K ₀ + K _S .P _FG (6)

where K _{0 is} a zero point shift and K _{S is} a slope. The zero point shift K ₀ and the slope K _S are dependent on the speed N, the intake manifold geometry and the stroke of the intake and exhaust valves 30 , 31 .

In order to set the air mass flow MAF, a corresponding opening degree of the throttle valve 10 must be set. The flow through the throttle point in the intake tract 1 at the throttle valve 10 is for subcritical operation by the equation

modeled with

and χ adiabatic exponent, R specific gas constant, where equation (3) inserted in ( 8 ) gives:

The equation (7) is solved after the reduced flow cross section ARED_THR at the throttle valve 10 and the equations (6), (5) and (9) are used. This results in the following equation for the reduced flow cross section ARED_THR

The reduced flow cross section ARED_THR at the throttle valve 10 is calculated in the second pilot control device 62 in accordance with equation (10). The estimated value AMP_MOD of the ambient pressure is used for the ambient pressure AMP.

A second control device 64 is provided, the control variable of which is the exhaust gas recirculation rate and the control difference of which is the difference between the target value EGRR_SP and the actual value EGRR_AV of the exhaust gas recirculation rate. The second control device 64 is preferably designed as a PI controller. The control signal of the second control device is a correction value DARED_THR of the reduced flow cross section at the throttle valve 10 . The gain of the PI controller is preferably low, since this prevents the control signal from oscillating, but at the same time the exhaust gas recirculation rate is quickly set by the second pilot control device. A high driving comfort of a motor vehicle in which the internal combustion engine is arranged is achieved.

In a block B9, a setpoint THR_SP of the degree of opening of the throttle valve 10 is determined from a characteristic map depending on the sum of the correction value DARED_THR and the reduced flow cross section ARED_THR on the throttle valve 10 . The setpoint THR_SP is a not shown and generally known position controller of the throttle valve 10 leads.

A block B10 comprises a sequence control which coordinates the working of the first and second pilot control devices 61 , 62 and the first and second control devices depending on the target value EGRR_SP of the exhaust gas recirculation rate. The sequential control system assigns predefined values to logical variables LV_S_I, LV_S_II, LV_R_I, LV_R_II. Depending on the respective value of the logical variable which is assigned to the respective pre-control device or control device, the respective pre-control device or control device is activated or deactivated, or a predetermined output signal is present at its output.

In the preferred exemplary embodiment, the sequence control determines the values for the logical variables as a function of an actual value EGRR_AV of the opening degree of the exhaust gas recirculation valve 51 . As long as the actual value EGRV_AV of the degree of opening of the exhaust gas recirculation valve 41 is less than a predetermined threshold value, only the control device 63 and the first pilot control device 61 are activated. The throttle valve has a substantially maximum degree of opening. The exhaust gas recirculation rate is accordingly set in this area via the exhaust gas recirculation valve actuator 51 .

If the actual value EGRV_AV of the degree of opening of the exhaust gas recirculation valve 51 exceeds the predetermined threshold value, then the second control device 64 and the second pilot control device 62 are additionally activated. This results in a quick adjustment of the fresh gas partial pressure P _FG , which leads to an increase in the recirculated exhaust gas mass flow through the exhaust gas recirculation pipe 50 .

Maps are by stationary measurements on an engine test stand or determined in driving tests.

The invention is not based on the described embodiment limited game. For example, it is immaterial whether the Control device as a hard-wired circuit arrangement realized or in the form of a program by one Microprocessor is processed in a motor control.

Claims (8)

1. Device for controlling an internal combustion engine with a throttle valve ( 10 ) in an intake tract ( 1 ) and with an exhaust gas recirculation valve ( 51 ) in an exhaust gas recirculation device ( 5 ), in which
a first pilot control device ( 61 ) is provided, the control variable of which is the exhaust gas recirculation rate and which is associated with the exhaust gas recirculation valve ( 51 ) as an actuator,
a second pilot control device ( 62 ) is provided, the control variable of which is the exhaust gas recirculation rate and which is associated with the throttle valve ( 10 ) as an actuator, and
a first controller ( 63 ) is provided, the controlled variable of which is the exhaust gas recirculation rate and to which the exhaust gas recirculation valve ( 51 ) is assigned as an actuator. 2. Device for controlling an internal combustion engine with a throttle valve ( 10 ) in an intake tract ( 1 ) and with an exhaust gas recirculation valve ( 51 ) in an exhaust gas recirculation device ( 5 ), in which
a first pilot control device ( 61 ) is provided, the control variable of which is the exhaust gas recirculation rate and which is assigned to the exhaust gas recirculation valve ( 51 ) as an actuator, and
a second pilot control device ( 62 ) is provided, the control variable of which is the exhaust gas recirculation rate and which is associated with the throttle valve ( 10 ) as an actuator, and
a second controller ( 64 ) is provided, the controlled variable of which is the exhaust gas recirculation rate and the throttle valve ( 10 ) is assigned as an actuator. 3. Device according to one of claims 1 or 2, characterized in that a speed sensor ( 24 ) is provided which detects a speed (N), that a means for determining the ambient pressure (AMP) is provided and that the second pilot control device ( 61 ) control the throttle valve ( 10 ) depending on the speed (N) and the ambient pressure (AMP). 4. Device according to claim 1 or 2, characterized in that it has a sequence control (B10) which, depending on at least one operating variable of the internal combustion engine, activates or deactivates the first and / or the second pilot control ( 61 , 62 ). 5. Device according to claim 1 or 3, characterized in that it has a sequence control (B10) which, depending on at least one operating variable of the internal combustion engine, the first and / or the second pilot control ( 61 , 62 ) and / or the first controller ( 63 , 64 ) activated or deactivated. 6. Device according to claim 2 or 3, characterized in that it has a sequence control (B10) which, depending on at least one operating variable of the internal combustion engine, the first and / or the second pilot control ( 61 , 62 ) and / or the second controller ( 63 , 64 ) activated or deactivated. 7. Device according to one of the preceding claims, characterized in that it has an observer (B3), which calculates an estimated value (EGRMF_MOD) of the recirculated exhaust gas mass flow depending on at least one operating variable of the internal combustion engine, that it is assigned an air mass meter ( 12 ) is that it detects an air mass flow and an actual value (MAF_AV) of the air mass flow, and that it has a means for calculating an actual value (EGRR_AV) of the exhaust gas recirculation rate, which is the actual value (EGRR_AV) of the exhaust gas recirculation rate depending on the estimated value (EGRMF_MOD) of the recirculated exhaust gas mass flow and the actual value (MAF_AV) of the air mass flow. 8. Device according to one of the preceding claims, there characterized in that a setpoint (TQI_REQ) one in specified torque on an output shaft of the Brenn engine is derived from an accelerator pedal value (PV) and that a target value (EGRR_SP) depends on the exhaust gas recirculation rate gig of the setpoint (TQI_REQ) of the indicated torque and the accelerator pedal value (PV) is determined.